Recently we attended a risk-based seismic design and evaluation seminar and was surprised by the pushover model developed for seismic analyses / evaluation. We questioned if the model was intended to be used for analyses / evaluation, or was intended as a general case. The answer was the model is considered appropriate for analyses / evaluation.

One of our engineers commented the model was too crude; confirmed that required structural ductility could be computed from the equilibrium plot developed in the seminar; and wanted to limit the story displacement. My concern with the pushover model used for structural analyses / evaluation is:

1. The model is too crude to accept the resulting floor acceleration and story displacement.

2. The floor acceleration was determined to be higher at the second floor, not the roof.

3. The building is loaded into the inelastic range, therefore floor accelerations determined from the model based on an elastic distribution of seismic force between floors is unrealistic.

4. An evaluation of p-delta and inelastic effects may indicate the building is unsafe or even collapsed for the considered earthquake.

According to the seminar, there is an opinion the simple pushover model is adequate and acceptable and a more complex model may give false results since the true structural ductility is difficult to determine, i.e., inadequate connection detailing and accounting for member strength.